The present invention generally relates to printing on a hardcopy medium and more particularly relates to placing data within or adjacent the text or graphic printed on a hardcopy medium.
Inkjet printing is usually considered to be a technique of directing small discrete quanta of ink from a reservoir to a sheet or medium such as paper, transparency film, and the like to produce perceptible alphanumeric, graphic, and pictorial images on the medium. The energy needed to move the quanta of ink (ink drops, usually) can come from thermal, piezoelectric, electrostatic, acoustic, electromagnetic, and similar energy sources. The basics of inkjet printing technologies can be found in Output Hardcopy Devices, W. J. Lloyd and H. T. Taub (edited by R. C. Durbeck and S. Sherr), Academic Press, San Diego, 1988, chapter 13. The ink drops are deposited on the printed medium as dots of ink colorant from which the liquid ink vehicle quickly evaporates. For text, ink dots are deposited in an arrangement that produces a full colorant (usually black) presence where a character is to be printed and an absence of colorant in the spaces within and between the characters. Roughness of the edges of the printed character due to the quantum nature of each ink drop can be mitigated by careful selection of the placement of each drop at the character edge (as well as other optimizations of ink chemistry, media, and the like).
For gray scale printing and color image printing, the concept of printing in superpixels has come into being to enable gradations of intensity and hue to be realized. A superpixel is generally recognized to be a coordination of an area (the superpixel) of the printed medium, usually a theoretical square that is subdivided into smaller square areas. Into each of the smaller areas (referred to as pixels) a dot can be placed, or left unplaced, depending upon the level of gray scale or the color to be realized for the superpixel. See, for example, U.S. Pat. No. 4,930,018. Moreover, to avoid undesirable artifacts (Moiré patterns, “worms”, etc.) of printing using discrete quanta (dots), dithering and error diffusion calculations are made and the dots are distributed among the superpixels to reduce the artifacts in accordance with the calculations. See, for example, U.S. Pat. No. 5,031,050.
Generally without regard to the method of printing, others have begun to employ techniques of embedding information (data) into a printed image. In U.S. Pat. No. 5,905,819 the art of steganography was identified as a precursor to the more recent desire to hide a digital message within a printed image. Digital steganography was interpreted, there, as encompassing techniques of tamper-proofing (providing the ability to determine whether a digital image has been manipulated or modified from an original), digital watermarking (providing the ability to establish ownership and copyright infringement), image tagging (adding a unique identifier to each image copy to identify the individual creating bootleg copies), digital pointers (providing, for example, an invisible internet address for additional information), and data augmentation (providing, in a form relatively undetectable by human perception, additional information regarding the image in which the data is hiding). This patent discloses a complex method of combining the desired image and the data in a manner which disturbs the desired image very little. This disclosed method, however, suffers from the drawback that the original image must be known for the data to be recovered from the combined copy. Also see, for example, U.S. Pat. No. 5,859,920.
Hidden information in a visible image has also found usage in postal franking applications. In one instance, described in U.S. Pat. No. 5,829,895 where a two-pass dot matrix printing method is used to place a postal indicia on an envelope, one of the passes places a message in the printed postal indicia by adjusting the dot matrix dot density to create a lightly populated dot density, thereby enabling the message to be readable due to the low population of dots. The second printing pass places a higher dot density in the previously low dot population density area in order to obliterate the message. Postal franking fraud can thereby be avoided.
Other techniques of preventing postal fraud include the use of fluorescing (or phosphorescing) ink, which is invisible in the human-perceptible light spectrum, to be printed in a print layer over a visibly perceptible print layer. Thus, a bar code printed over the visible print (such as that described in U.S. Pat. No. 5,693,693) can contain more, and relatively secure, information than that available in a conventional bar code.
In a separate technological direction, InfoImaging Technologies, Inc. is presently marketing a product called 3D FaxFile. This product converts documents (text, color images, etc.) into a digital black and white pattern that can be transmitted via a standard fax machine. At the receiving end, the faxed document can be scanned or otherwise reconverted into a digital data stream that is subsequently recomposed into a copy of the original document. Coding and data compression can yield a secure and significantly smaller document to be faxed than the original. And, a color document can be transmitted by an otherwise colorless transmission technology.
The foregoing notwithstanding, there exists a need to provide a technique of adding information to or storing information on a printed medium. The use of color offers an expanded capability for higher information density than simple black and white printing. Moreover, if two or more blocks of information, which can be unrelated, are to be printed on the medium it is desirable that the information not interfere with each other and that each be independently recoverable from the printed medium.